Flashing color sequence annunciator system with fail-safe features

ABSTRACT

An annunciator system having a plurality of remote sensors for detecting normal and abnormal conditions and a central annunciator station. The annunciator station includes a plurality of visual annunciators corresponding to respective remote sensors. Each annunciator has alarm signalling means for providing alternate red and white flashing light signalling to indicate an abnormal condition, acknowledge signalling means responsive to manual acknowledge operation for providing steady red light signalling, return-to-normal signalling means for providing steady green light signalling to indicate a normal condition following an abnormal condition, and reset means responsive to manual reset operation for causing the steady green light signalling to cease. The central annunciator station further includes at least one flasher means and means responsive to failure of the flasher to provide unique light signalling.

[4 1 Jul 1,1975

ABSTRACT ignal- H 1 I 1 1 i 1 I I 1 1 I 1 1 I W I 1 1 I 111. 0 u T 0 WA. i W 7. 1?

To OTHER ANNUNCIATORS AND REMOTE SENSORS l /i E 1 2/; i I 1 I l 4/4: 5M; 1 1 a .4

15 Claims, 1 Drawing Figure United States Patent Kessler An annunciator system having a plurality of remote sensors for detecting normal and abnormal conditions and a central annunciator station. The annunciator FLASHING COLOR SEQUENCE ANNUNCIATOR SYSTEM WITH FAIL-SAFE FEATURES [75] Inventor: Arthur R. Kessler, St. Louis, Mo.

station includes a plurality of visual annunciators cor- [73] Assignee: Electro Devices, Inc., St. Louis, Mo.

Filed: Nov. 19, 1973 Appl. No.: 417,037

responding to respective remote sensors. Each annunciator has alarm signalling means for providing alternate red and white flashing light signalling to indicate an abnormal condition, acknowledge signalling means responsive to manual acknowledge operation for providing steady red light signalling, return-to-normal si nalling means for providing steady green light 5 .rw 3 .0 1 .0 2 4 0 3 4 u 3 mmhu .c r 3 .8 "m L C0 S .M U mlm IF 1111. 2 8 w ling to indicate a normal condition following an abnormal condition, and reset means responsive to manual reset operation for causing the steady green light signalling to cease. The central annunciator station fur- 340/2l3.2 ther includes at least one flasher means and means re- 340/213.2 sponsive to failure of the flasher to provide unique li ht si nallin 340/2132 g g g 2,730,702 Marmarstone................... 3,107,349 3,287,717 Kraus.....

Primary Examiner-Thomas B. l-labecker Attorney, Agent, or Firm-Koenig, Senniger, Powers and Leavitt 1 FLASHING COLOR SEQUENCE ANNUNCIATOR SYSTEM WITH FAIL-SAFE'FEATURES BACKGROUND OF THE INVENTION This invention relates to annunciator systems and more particularly to a flashing color'sequence annunciator system which provides a unique signalling indication if the flasher should fail.

Annunciator systems provide various types of visual indication for normal, alarm, acknowledge, and clear (return-to-normal) conditions. In a flashing single color sequence, for example, a visual indicator provides no signal during a normal condition, a flashing white signal when an alarm condition is detected, a steady white signal when the alarm condition is acknowledged and a return to a no signal either automatically or manually after clearing of the alarm condition. Flashing two color, steady two color, and steady three color (in which three colored lamps provide unique visual indication for each condition) sequences are also used. Audible indication is often used in conjunction with visual indication.

Most flashing sequence systems employ a single flasher to control a multiplicity of annunciators or alarm point modules, usually in the order of 30 to 50. The flasher may fail in either a closed or open mode. Flasher failure in one mode precludes any visual indica-- tion during an alarm condition while failure in the other mode causes a steady light signalling during an alarm condition duplicating the light signalling associated with a different condition. Thus flasher failure typically results in a false indication or no indication and thus misleads or delays the operator in initiating remedial action possibly causing serious consequences.

While steady three color sequences provide a unique visual indication for each condition, they lack the feature of providing a flashing indication in an alarm condition to command operator attention.

SUMMARY OF THE INVENTION Among the several objects of this inventionmay be noted the provision ofa flashing color sequence annunciator systm and method of visual annunciator signalling which provides unique signalling for normal, acknowledge, and clear conditions and flashing color signalling during an abnormal condition and which upon failure of the flasher provides visual signalling during an alarm condition not duplicative of the visual signalling associated with any other condition; the provision of such an annunciator system which includes ahighly reliable flasher that, in the event of failure, is more likely to' fail in an open mode than in a closed mode; and the provision of such an annunciator system which has a normal condition in whichlamps of different colors are energized in series thereby to continuously monitor their condition and thereby to provide a positive indication of lamp burn-out.

Briefly, an annunciator system of the present invention has a plurality of remote sensors for detecting normal and abnormal conditions and a central annunciator station. The annunciator station includes a plurality of A operation for providing steady red light signalling, re- A turn-to-norrnal signalling means for providing steady green light signalling to indicate a normal condition following an abnormal condition, and reset means responsive to manual reset operation for causing the steady green light signalling to cease. The annunciator station further includes at least one flasher means and means responsive to failure of the flasher to provide unique light signalling.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a schematic circuit diagram of an annunciator system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, a flashing color sequence annunciator system is schematically depicted in simplified form illustrating a single annunciator or alarm point module. It comprises a remote sensor 1, a visual annunciator 3, and a flasher 5. The annunciator is commonly connected to both the remote sensor and the flasher by respective pairs of leads Ll,L2 and L3,L4. The drawing also shows an optional audible alarm or indicator 6 connected to the annunciator via a pair of leads L5,L6. DC. power at a suitable voltage is supplied to the annunciator by a pair ofbusses l-V, -V. It is tobe understood that in most applicationsan annunciator system would include a plurality of remote sensors conne cted to corresponding visual annunciators along with a single flasher and audible indicator.

Each remote sensor comprises sensing contacts which are either normally open or normally closed; Re mote sensors monitor various conditions such as temperature, pressure, position, or other conditions. When there is an out-of-Iimit condition such as an abnormal pressure, etc., operation of the sensing contacts of a sensor causes out-of-limit alarm indication at the respective annunciator associated with that'sensorf The detailed circuitry of an zannunciator is described in detail hereinbelow. For the present, however, it is sufficient to note that the annunciator system generally includes a panel arrangement wherein the respective annunciators each have an indicator providing flashing or steady colored light indication. These indicator pan els are arrangedin suitable manner for being observed by supervisory personnel at a control facility.

An important feature of this invention lies in' the ability of the respective annunciators to provide unique visual indication of various conditions despite flasher failure A set of'colored lamps (red, white and green) designated R, W, and G is used to produce the various visual indications, During a normal condition the annunciator connects the three lamps in series to provide a dim white light thereby positively indicating that each of the three lamps is still operative. Under an alarm condition, a respective annunciator will effect a flashing red and white light signalling (unless there is flasher failure in which event a unique steady bright whitelight signalling will be provided). When the operator ac-' knowledges the alarm condition by actuation of a normally open momentary contact pushbutton.PB1, the annunciator exhibits steady red light signalling. Upon abatement of the out-of-limit condition, the annunciator will provide a steady green light indication. Finally the operator will reset the annunciator to a normal condition by actuation of a normally open momentary contact pushbutton' PB2.

As remote sensor 1 may be either a normally open or normally closed type sensor, a two position switch SW1 is provided to adapt the respective annunciator to the type of sensor connected therewith. When a normally open sensor is used and SW] is in the NO position dur ing a normal condition, the coil of a relay RS having a normally open contact RS1 will remain deenergized preventing positive voltage +V from being applied via conductor 8 to a bus 9. When bus 9 is deenergized, the green G, white W, and red R lamps are energized by being series-connected between the positive voltage bus +V and the negative bus -V thereby providing dim white light signalling.

Upon detection of an abnormal condition, the sensing contacts of remote sensor 1 will close energizing the coil of relay RS. Normally open contact RS1 will close causing positive voltage via conductor 8 to be applied to bus 9. One side of the coil of relay RS is connected to a contact of the remote sensor 1 through a diode D1 and the right-hand wiper of SW1 while the other side of the coil of RS is connected to the negative bus V through a current limiting resistor R1. A capacitor C1 is connected across the coil of RS to protect the coil against possible transient voltage peaks.

Further circuitry of the annunciator may logically be broken down into means or sections foreffecting alarm signalling, acknowledge signalling, return'to-normal signalling, and reset or normal signalling.

In the alarm signalling section of the circuitry, a diode D5 has its anode connected to bus 9 and its cathode is commonly connected to a junction between the red R and white W lamps, the red lamp being further connected to negative voltage bus -V. The junction between white and green G lamps is commonly connected to negative voltage bus V through a series circuit comprising a diode D8, a silicon controlled rectifier (SCR) SCR2, and another diode D9. The remaining terminal of green lamp G is connected to positive voltage bus +V.

.Further circuitry in the alarm signalling section includes a gate circuit for SCR2 in which resistors R5, R6, R7 and R9 are connected in a series-parallel combination from bus 9 to negativevoltage bus -V. Capacitors C5 and C8 are respectively connected from the gate and anode of SCR2 to -V to bypass any transient voltage spikes. A flasher capacitor C7, connected to V through a resistor R14 and a diode D10 and connected to the flasher through a diode D12 and lead L3, controls conduction of SCR2 when gated. The circuitry of the flasher will be described hereinafter, but for the present suffice it to say that the flasher operates when an abnormal condition is detected to clamp and unclamp C7 to positive voltage supplied by bus 9 through a resistor R11 and a diode D11.

When an abnormal condition is sensed the red lamp is immediately energized. Also SCR2 is gated on energizing both the white and green lamps. Though all three lamps are then illuminated behind the usual annunciator panel, the white lamp is brighter and the colors red and green tend to complement each other. Thus only a white signal appears to be given. When the flasher operates to unclamp C7 from +V, C7 discharges through a path including D12, the flasher, the negative bus, D9, and SCR2. This causes a reverse current through SCR2 turning it off and extinguishing the white and green lamps. Gating on of SCR2 is prevented because the gate circuit of SCR2 is disabled by operation ofa diode D4 connected from resistor R5 to diode D12.

The flasher 5 is essentially a square wave generator with a frequency of sixty cycles per minute. A unijunction transistor UJT controls operation of the flasher. The unijunction transistor has one base connected to +V through resistors R20 and R22 while its other base is connected directly to V. A zener diode ZD is connected in parallel across UJT to provide voltage regulation. The flasher has a dual output comprising silicon controlled rectifiers SCR3 and SCR4. Each output has the capacity of controlling up to approximately 30 annunciators. Resistor 20 is commonly connected to the gates of SCR3 and SCR4 and the emitter of UJT through resistors R19, R18 and R21 respectively. The gates of SCR3 and SCR4 are also connected to the emitter of UJT through a capacitor C11 and a capacitor C12, and a capacitor C10 and C12 respectively.

The unijunction transistor operates to generate pulses continuously. When capacitor combinations C11, C12 and C10, C12 charge to increase the emitter voltage of the UJT sufficiently, the unijunction transistor conducts decreasing the voltage at the gates of SCR3 and SCR4. The capacitor combinations discharge path includes the unijunction transistor and the cathode-gate circuits of SCR3 and SCR4. As the capacitors discharge, the emitter voltage of the unijunction transistor will drop to a point such that UJT will no longer conduct thereby permitting gate signals to be provided to SCR3 and SCR4 and allowing the capacitor combinations to recharge.

Although gate signals are applied to SCR3 every second, it will not conduct until a positive voltage is applied to its anode, i.e., when the remote sensor detects an out-of-limit condition. At that time it will conduct allowing capacitor C7 to discharge. However as C7 discharges and the gate signal is removed by operation of the UJT, SCR3 will turn off when the current flowing through it drops below the holding current.

The flasher is completely solid state providing high reliability, however, some possibility of failure exists. Since the UJT operates continuously while SCR3 operates only during an abnormal condition, failure of the UJT is more likely. Most failures in unijunction transistors are caused by the breakdown, or carbonization, of the junction rendering the transistor conductive. In this application if the UJT fails so that it conducts all the time, no gate signal is provided to SCR3. Therefore, the probability of flasher in the open mode, SCR3 not conducting, is greater than the probability of flasher failure in the closed mode, SCR3 conducting.

If the flasher has failed in an open mode and an abnormal condition is detected, SCR2 will be energized providing steady bright white light signalling. As will be seen later, this is unique visual indication of flasher failure in an alarm condition because under no other condition (normal, reset, etc.) is a steady bright white signal provided. However even if the flasher fails in a closed mode (SCR3 is conducting) prior to detection of an abnormal condition, although D4 disables the normal SCR2 gate circuit, an energization bypass means comprising a resistor R17 and a capacitor C9 connected in parallel from bus 9 to the gate of SCR2 provides a pulse to the gate of SCR2 when an 0ut-oflimit condition occurs. Thus SCR2 becomes energized again providing unique bright white light signalling so that failure of the flasher is again visually signalled.

In the extremely improbably situation in which SCR3 would fail in a closed mode just after an abnormal condition is detected, although SCR2 would be prevented from turning on the white and green lamps, the red lamp would light affording the operator at least some visual indication of an abnormal condition and where it existed. If this condition occured in the old flashing white sequence, there would be no visual indication and the out-of-limit condition would go undetected and possibly result in a generator failure, etc.

In the section of the annunciator circuitry comprising acknowledge signalling means, a further silicon controlled rectifier SCRl has its anode connected to bus 9 through a resistor R4 while its cathode is connected directly to the negative bus. Thus positive voltage is applied to the anode of SCRl up detection of an abnormal condition by a respective remote sensor. When the acknowledge pushbutton switch P81 is actuated, the gate circuit of SCR 1, constituted by series resistors R2 and R3 connected from FBI to the negative bus applies a positive signal to the gate of SCRl turning it on. Capacitors C2 and C3 are used to shunt any possible transient voltage spikes'away from the gate of SCRl to the negative bus and from the anode of SCRl to the negative bus, respectively.

When SCRl turns on, it turns off SCR2 by discharging capacitor C7 through a path including a diode D2, SCRl, the negative bus, D9 and SCR2 causing current to flow through SCR2 in the reverse direction and causing the anode current of SCR2 to drop to less than the holding current. Since SCR2 has been turned off the white W and green G lamps are extinguished and only the red R lamp remains illuminated thus indicating the alarm signal has been acknowledged.

While the remote sensor contacts remain closed, a capacitor C6 is charged through a resistor R12. One side of C6 is commonly connected to a resistor R10, the cathode of SCR2 and, via a further resistor R13, to V. When the out-of-limit condition is corrected, the contacts of the remote sensor open, deenergizing relay RS and bus 9, thus allowing capacitor C6 to discharge through a path including a resistor R16 and resistor R13 to V. As current flows through R13, the cathode of SCR2 is temporarily made negative with respect to its gate electrode, triggering SCR2. This energizes the green lamp but neither the red nor white lamp is illuminated because bus 9 is no longer connected to positive voltage inasmuch as RS1 has been opened. Capacitor C6 along with resistors R12, R13 and R16 comprises return-to-normal signalling means.

The operator returns the annunciator to normal condition by actuating normally open momentary contact pushbutton PB2. PB2 connects capacitor C7 to +V via a diode D13 and a resistor R15, and simultaneously supplies positive voltage through diode D12 and lead L3 to the anode of flasher circuit silicon controlled rectifier SCR3. When the unijunction transistor next gates SCR3, capacitor C7 discharges through SCR2 turning SCR2 off. At this time the red R, white W and green G lamps are concommitantly energized by connection in series across the voltage source to provide dim white light signalling.

Testing of the annunciator may be accomplished by depressing a normally open momentary contact pushbutton PB3 which connects the positive bus to bus 9. If operation is proper, SCR3 is triggered and the flasher is energized causing flashing red and white lamp illumination. Resetting is then accomplished by depressing pushbutton PB2 as described above.

As previously noted, the visual annunciator may be used in conjunction with audible indicator 6 to provide an aural warning. Bus 9 is connected to the audible indicator through a capacitor C4, a resistor R8, a diode D6, and lead L5. SCR2 is connected to the audible indicator via lead L6. Although the internal circuitry of the audible indicator is not shown, suffice it to say that the audible indicator is employed to provide aural warning during both an alarm condition and a returnto-normal condition. The aural warning in the alarm condition is silenced when the acknowledge pushbutton is actuated, and the aural indication in the returnto-normal condition abates when the reset pushbutton PB2 is actuated.

In operation of the flashing color sequence annunciator system, it is assumed that remote sensor 1 is open, there being initially no out-of-limit condition. During a normal condition the red R, white W, and green G lamps are energized in series producing dim white light signalling thereby providing a positive indication of lamp burn-out. When an abnormal condition is sensed, the contacts of the remote sensor close energizing bus 9. Red and white flashing light signalling is effected (unless there is flasher failure in which event a unique steady bright white light signalling will be provided).

Upon manual acknowledge of an alarm condition by actuation of pushbutton PBl, the flashing red and white signalling is stopped and a steady red light signal is exhibited. When out-of-limit condition is corrected, the contacts of the remote sensor open deenergizing bus 9 and causing the steady red light signal to cease and a steady green signal to appear in the indicator panel.

Finally the operator will actuate pushbutton PB2 resetting the annunciator to a normal condition causing the steady bright green light signalling to go out and energizing all three lamps in series providing a dim white light signalling, a positive indication that the filament of each lamp is operative.

Thus a unique light signalling is generally provided for each condition without regard to the condition of the flasher providing the operator direct indication of the status of each remote sensor. If the flasher is functioning properly, a flashing twocolor light signal is exhibited in the alarm condition to quickly command operator attention.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An annunciator system comprising a plurality of remote sensors for detecting normal and abnormal conditions and a central annunciator station to which said remote sensors are connected by leads, said annunciator station including a plurality of visual annunciators corresponding to respective remote sensors, each of said annunciators comprising alarm signalling means for providing alternate red and white flashing light signalling upon detection by the respective sensor of an abnormal condition, acknowledge signalling means responsive to manual acknowledge operation for causing the alternate red and white flashing light signalling to cease and for providing steady red light signalling, return-to-normal signalling means responsive to detection by the respective sensor of a normal condition following an abnormal condition for causing the steady red light signalling to cease and for providing steady green light signalling and reset means responsive to manual reset operation for causing the steady green light signalling to cease, said annunciator station further including at least one flasher means for effecting said alternate red and white flashing light signalling by the alarm means of respective annunciators, and means responsive'to failure of said flasher during detection by a respective sensor of an abnormal condition to cause bright white light alarm signalling by the respective annunciator and thereby provide unique light signalling in the event of failure of the flasher means.

2. An annunciator system as set forth in claim 1 wherein each of said visual annunciators comprises white, red and green light sources for providing said light signalling.

3. An annunciator system as set forth in claim 2 wherein each of said visual annunciators comprises normal condition indicator means for causing dim white light signalling to be provided by .said light sources in response to manual operation of said reset means.-

4.-An annunciator system as set forth in claim 3 wherein said white, red and green light sources comprise respective incandescent bulbs, said white, red and green sources being concomitantly energized by connection in parallel across a voltage source to provide said bright white light signalling, said red bulb being connected solely across the voltage source to provide said red light signalling, said green bulb being connected solely across the voltage source to provide said green light signalling, and said white, red and green bulbs concomitantly energized by connection in series across the voltage source to provide said dim white light signalling.

5. An annunciator system as set forth in claim 4 wherein said red and white flashing light signalling is provided by means for alternately energizing and deenergizing both of said white and green bulbs simultaneously while said red bulb remains energized.

6. An annunciator system as set forth in claim 1, said central annunciator station further comprising audible warning means for providing first audible signalling upon detection by any of said sensors of an abnormal condition; said audible signalling being terminated by said manual acknowledge operation, said audible means providing further audible signalling in response to a normal-condition being detected by any of said sensors following said first audible signalling, said further audible signalling being terminated by said manual reset operation.

7. An annunciator system as set forth in claim 5 wherein said means responsive to flasher failure includes said silicon controlled rectifier and provides said bright white alarm signalling by causing concomitant energization of said white, red, and green light sources in parallel across said voltage source.

8. An annunciator system as set forth in claim 1 wherein each of said annunciators further includes an energization bypass means which insures said unique light signalling upon detection by the respective sensor of an abnormal condition if the flasher means has failed in a closed mode. v

9. An annunciator system as set forth in claim 1 wherein said flasher means is solid state and highly reliable and wherein said flasher means has a higher probability of failure in the open mode than in the closed mode.

10. Annunciator apparatus for use in an annunciator system having at least one remote sensor for detecting normal and abnormal conditions, said annunciator apparatus being controlled by said sensor and comprising:

a plurality of light sources for providing first, second and third color light signals;

means responsive to detection by said sensor of an' abnormal condition for energizing preselected ones of the light sources to provide flashing light signals alternating between two of said colors thereby to provide alarm indication;

acknowledge means adapted to be manually actuated for acknowledging the alarm indication;

means responsive to actuation of said acknowledge means for terminating said flashing light signals and for energizing one of said light sources to provide a steady light signal of one of said colors thereby to provide an acknowledge indication;

means responsive to detection by the sensor of a normal condition for deenergizing the last-said light source and for energizing a further one of the light sources to provide a steady light signal of another color thereby to provide a return-to-normal indication;

reset means adapted to be manually actuated for resetting the annunciator apparatus; means responsive to actuation of said reset means for deenergizing said further light source and thereby terminating said return-to-normal indication; and

flasher means for causing said flashing light signals to be provided, said flasher means being subject to failure, and means for causing an unique signalling indication to be provided upon failure of said flasher means during detection by'the sensor of an abnormal condition.

11. Annunciator apparatus as set forth in claim 10 wherein said unique signalling indication is bright white, the color providing the acknowledge indication is red, and the color providing the return-to-normal indication is green, and wherein said flashing light signals alternate between the colors of white and red.

12. Annunciator apparatus as set forth in claim 10 wherein said means responsive to actuation of said reset means is operative to cause said light sources to provide a dim steady light thereby to provide a normal condition indication.

13. Annunicator apparatus as set forth in claim 11 wherein said means for providing said unique bright white signalling indication includes a silicon controlled rectifier and is operative to cause concomitant energization of said plurality of light sources thereby to provide unique visual indication of an abnormal condition in the event of failure of said flasher means.

14. A method of visual annunciator signalling for use in an annunciator system having a plurality of remote sensors for detecting normal and adnormal conditions and a plurality of annunciators corresponding to respective remote sensors, said method comprising providing alarm indication by a flasher which effects alternate red and white flashing light signalling by an annunciator in response to detection by the respective sensor of an abnormal condition, providing acknowledge indication by ceasing said alternate red and white flashing light signalling and thereupon providing steady red light signalling by the annunciator thereby to acknowledge said detection of an abnormal condition, ceasing said steady red light signalling and thereupon providing return-to-normal signalling by steady green light signalling by the annunciator in response to detection of the respective sensor of a normal condition following an 

1. An annunciator system comprising a plurality of remote sensors for detecting normal and abnormal conditions and a central annunciator station to which said remote sensors are connected by leads, said annunciator station including a plurality of visual annunciators corresponding to respective remote sensors, each of said annunciators comprising alarm signalling means for providing alternate red and white flashing light signalling upon detection by the respective sensor of an abnormal condition, acknowledge signalling means responsive to manual acknowledge operation for causing the alternate red and white flashing light signalling to cease and for providing steady red light signalling, return-to-normal signalling means responsive to detection by the respective sensor of a normal condition following an abnormal condition for causing the steady red light signalling to cease and for providing steady green light signalling and reset means responsive to manual reset operation for causing the steady green light signalling to cease, said annunciator station further including at least one flasher means for effecting said alternate red and white flashing light signalling by the alarm means of respective annunciators, and means responsive to failure of said flasher during detection by a respective sensor of an abnormal condition to cause bright white light alarm signalling by the respective annunciator and thereby provide unique light signalling in the event of failure of the flasher means.
 2. An annunciator system as set forth in claim 1 wherein each of said visual annunciators comprises white, red and green light sources for providing said light signalling.
 3. An annunciator system as set forth in claim 2 wherein each of said visual annunciators comprises normal condition indicator means for causing dim white light signalling to be provided by said light sources in response to manual operation of said reset means.
 4. An annunciator system as set forth in claim 3 wherein said white, red and green light sources comprise respective incandescent bulbs, said white, red and green sourceS being concomitantly energized by connection in parallel across a voltage source to provide said bright white light signalling, said red bulb being connected solely across the voltage source to provide said red light signalling, said green bulb being connected solely across the voltage source to provide said green light signalling, and said white, red and green bulbs concomitantly energized by connection in series across the voltage source to provide said dim white light signalling.
 5. An annunciator system as set forth in claim 4 wherein said red and white flashing light signalling is provided by means for alternately energizing and deenergizing both of said white and green bulbs simultaneously while said red bulb remains energized.
 6. An annunciator system as set forth in claim 1, said central annunciator station further comprising audible warning means for providing first audible signalling upon detection by any of said sensors of an abnormal condition, said audible signalling being terminated by said manual acknowledge operation, said audible means providing further audible signalling in response to a normal condition being detected by any of said sensors following said first audible signalling, said further audible signalling being terminated by said manual reset operation.
 7. An annunciator system as set forth in claim 5 wherein said means responsive to flasher failure includes said silicon controlled rectifier and provides said bright white alarm signalling by causing concomitant energization of said white, red, and green light sources in parallel across said voltage source.
 8. An annunciator system as set forth in claim 1 wherein each of said annunciators further includes an energization bypass means which insures said unique light signalling upon detection by the respective sensor of an abnormal condition if the flasher means has failed in a closed mode.
 9. An annunciator system as set forth in claim 1 wherein said flasher means is solid state and highly reliable and wherein said flasher means has a higher probability of failure in the open mode than in the closed mode.
 10. Annunciator apparatus for use in an annunciator system having at least one remote sensor for detecting normal and abnormal conditions, said annunciator apparatus being controlled by said sensor and comprising: a plurality of light sources for providing first, second and third color light signals; means responsive to detection by said sensor of an abnormal condition for energizing preselected ones of the light sources to provide flashing light signals alternating between two of said colors thereby to provide alarm indication; acknowledge means adapted to be manually actuated for acknowledging the alarm indication; means responsive to actuation of said acknowledge means for terminating said flashing light signals and for energizing one of said light sources to provide a steady light signal of one of said colors thereby to provide an acknowledge indication; means responsive to detection by the sensor of a normal condition for deenergizing the last-said light source and for energizing a further one of the light sources to provide a steady light signal of another color thereby to provide a return-to-normal indication; reset means adapted to be manually actuated for resetting the annunciator apparatus; means responsive to actuation of said reset means for deenergizing said further light source and thereby terminating said return-to-normal indication; and flasher means for causing said flashing light signals to be provided, said flasher means being subject to failure, and means for causing an unique signalling indication to be provided upon failure of said flasher means during detection by the sensor of an abnormal condition.
 11. Annunciator apparatus as set forth in claim 10 wherein said unique signalling indication is bright white, the color providing the acknowledge indication is red, and the color providing the return-to-normal indIcation is green, and wherein said flashing light signals alternate between the colors of white and red.
 12. Annunciator apparatus as set forth in claim 10 wherein said means responsive to actuation of said reset means is operative to cause said light sources to provide a dim steady light thereby to provide a normal condition indication.
 13. Annunicator apparatus as set forth in claim 11 wherein said means for providing said unique bright white signalling indication includes a silicon controlled rectifier and is operative to cause concomitant energization of said plurality of light sources thereby to provide unique visual indication of an abnormal condition in the event of failure of said flasher means.
 14. A method of visual annunciator signalling for use in an annunciator system having a plurality of remote sensors for detecting normal and adnormal conditions and a plurality of annunciators corresponding to respective remote sensors, said method comprising providing alarm indication by a flasher which effects alternate red and white flashing light signalling by an annunciator in response to detection by the respective sensor of an abnormal condition, providing acknowledge indication by ceasing said alternate red and white flashing light signalling and thereupon providing steady red light signalling by the annunciator thereby to acknowledge said detection of an abnormal condition, ceasing said steady red light signalling and thereupon providing return-to-normal signalling by steady green light signalling by the annunciator in response to detection of the respective sensor of a normal condition following an abnormal condition, providing reset indication by ceasing said steady green light signalling thereby to reset the annunciator for a subsequent alarm indication, and effecting during said alarm indication a steady bright white light signalling upon failure of the flasher.
 15. A method of visual annunciator signalling as set forth in claim 14 further comprising the step of providing normal condition indication following said reset indication by steady dim white light signalling. 